Flush toilets for discharging waste by flushing with flush water supplied from a flush water source have been known for some time in which, as noted in Patent Document 1 (Japanese Patent Unexamined Publication No. 2013-44177, for example, the rim spout port of a rim water passageway for forming a circulating flow by spouting flush water onto the shelf portion of a bowl is formed in the front area of the bowl, and a portion only of the rim inner circumferential surface is formed as an inward overhang in the water passageway immediately behind this rim spout port.
In addition, as noted in Patent Document 2 (Japanese Patent No. 5483314 (Japanese Patent Unexamined Publication No. 2011-12508)), flush toilets are also known in which the dimension in the vertical direction of the rim passage formed on the top edge of the bowl is set to become gradually smaller toward the downstream side.
However in conventional flush toilets set forth in the above-described Patent Documents 1 and 2, the cross sectional area of the water passing cross section in the water passageway formed at the downstream side of the rim spouting port is not set to be constant from the rim spout port toward the downstream side, therefore when the height of the water passage cross section on the downstream side of the rim spouting port is set to increase with distance downstream, there is a risk of turbulence in the rim spout water passing through the water passage cross section, and of flush water splashing.
Another problem is that visibility and cleanability of the water passageway on the downstream side of the rim spouting port degrades more as the area of the overhang portion covering the water passageway on the downstream side of the rim spouting port increases.